Once you have covered the preceding sections of this unit (Overview, Why this Science Matters, Study Guide), check to see what you have learned by answering the following questions.

1. What is a glycan?
   
   
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   A polysaccharide; the carbohydrate portion of a glycoconjugate, such as a glycolipid or glycoprotein.

2. Describe the basic structural chemistry of sialic acid.
   
   
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   All sialic acids have nine carbons, a carboxylic acid residue, and a variety of linkages to the underlying sugar chain.

3. If there are 21 amino acids and only 10 major monosaccharides in eukaryotes, why are there so many more possible combinations of monosaccharides in a hexasaccharide than amino acids in a hexapeptide?
   
   
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   Peptides are limited to linear arrangements of amino acids via peptide bonds. Saccharides are capable of forming both linear and branched molecules via multiple bond types. This difference leads to greater than 1.05 x 10E12 possible hexasaccharides molecules which is seven orders of magnitude greater than the number of possible hexapeptide molecules.

4. What two molecules would be likely targets for an influenza vaccine and why?
   
   
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   Haemagglutinin and neuraminidase because interference with either of these two proteins would disrupt the infection cycle of the virus.